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Message-ID: <3bada85ea59a20e68367f8ea98355dc76f31e42f.camel@kernel.org>
Subject: Re: [PATCH] nfsd: properly tear down server when write_ports fails
From: Jeff Layton <jlayton@kernel.org>
To: NeilBrown <neilb@suse.de>, Chuck Lever <chuck.lever@oracle.com>
Cc: Olga Kornievskaia <kolga@netapp.com>, Dai Ngo <Dai.Ngo@oracle.com>, Tom
 Talpey <tom@talpey.com>, linux-nfs@vger.kernel.org,
 linux-kernel@vger.kernel.org, Zhi Li <yieli@redhat.com>
Date: Wed, 13 Dec 2023 09:26:33 -0500
In-Reply-To: <170243914810.12910.1721447953189600231@noble.neil.brown.name>
References: <20231211-nfsd-fixes-v1-1-c87a802f4977@kernel.org>
	, <170233558429.12910.17902271117186364002@noble.neil.brown.name>
	, <a2b59634a697ae07a315d6f663afaff5cd5bf375.camel@kernel.org>
	, <ZXhlNtQ9o+howGbH@tissot.1015granger.net>
	, <ZXhot6zUt6G1xaos@tissot.1015granger.net>
	 <170243914810.12910.1721447953189600231@noble.neil.brown.name>
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On Wed, 2023-12-13 at 14:45 +1100, NeilBrown wrote:
> On Wed, 13 Dec 2023, Chuck Lever wrote:
> > On Tue, Dec 12, 2023 at 08:50:46AM -0500, Chuck Lever wrote:
> > > On Mon, Dec 11, 2023 at 06:11:04PM -0500, Jeff Layton wrote:
> > > > On Tue, 2023-12-12 at 09:59 +1100, NeilBrown wrote:
> > > > > On Tue, 12 Dec 2023, Jeff Layton wrote:
> > > > > > When the initial write to the "portlist" file fails, we'll curr=
ently put
> > > > > > the reference to the nn->nfsd_serv, but leave the pointer intac=
t. This
> > > > > > leads to a UAF if someone tries to write to "portlist" again.
> > > > > >=20
> > > > > > Simple reproducer, from a host with nfsd shut down:
> > > > > >=20
> > > > > >     # echo "foo 2049" > /proc/fs/nfsd/portlist
> > > > > >     # echo "foo 2049" > /proc/fs/nfsd/portlist
> > > > > >=20
> > > > > > The kernel will oops on the second one when it trips over the d=
angling
> > > > > > nn->nfsd_serv pointer. There is a similar bug in __write_ports_=
addfd.
> > > > > >=20
> > > > > > This patch fixes it by adding some extra logic to nfsd_put to e=
nsure
> > > > > > that nfsd_last_thread is called prior to putting the reference =
when the
> > > > > > conditions are right.
> > > > > >=20
> > > > > > Fixes: 9f28a971ee9f ("nfsd: separate nfsd_last_thread() from nf=
sd_put()")
> > > > > > Closes: https://issues.redhat.com/browse/RHEL-19081
> > > > > > Reported-by: Zhi Li <yieli@redhat.com>
> > > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > > > > > ---
> > > > > > This should probably go to stable, but we'll need to backport f=
or v6.6
> > > > > > since older kernels don't have nfsd_nl_rpc_status_get_done. We =
should
> > > > > > just be able to drop that hunk though.
> > > > > > ---
> > > > > >  fs/nfsd/nfsctl.c | 32 ++++++++++++++++++++++++++++----
> > > > > >  fs/nfsd/nfsd.h   |  8 +-------
> > > > > >  fs/nfsd/nfssvc.c |  2 +-
> > > > > >  3 files changed, 30 insertions(+), 12 deletions(-)
> > > > >=20
> > > > > This is much the same as
> > > > >=20
> > > > > https://lore.kernel.org/linux-nfs/20231030011247.9794-2-neilb@sus=
e.de/
> > > > >=20
> > > > > It seems that didn't land.  Maybe I dropped the ball...
> > > >=20
> > > > Indeed it is. I thought the problem seemed familiar. Your set is
> > > > considerably more comprehensive. Looks like I even sent some Review=
ed-
> > > > bys when you sent it.
> > > >=20
> > > > Chuck, can we get these in or was there a problem with them?
> > >=20
> > > Offhand, I'd say either I was waiting for some review comments
> > > to be addressed or the mail got lost (vger or Exchange or I
> > > accidentally deleted the series). I'll go take a look.
> >=20
> > I reviewed the thread:
> >=20
> > https://lore.kernel.org/linux-nfs/20231030011247.9794-1-neilb@suse.de/
> >=20
> > From the looks of it, I was expecting Neil to address a couple of
> > review comments and repost. These are the two comments that stand
> > out to me now:
> >=20
> > On 1/5:
> >=20
> > > > Then let's add
> > > >=20
> > > > Fixes: ec52361df99b ("SUNRPC: stop using ->sv_nrthreads as a refcou=
nt")
> > > >=20
> > > > to this one, since it addresses a crasher seen in the wild.
> > >=20
> > > Sounds good.
> > >=20
> > > > > but it won't fix the hinky error cleanup in nfsd_svc. It looks li=
ke that
> > > > > does get fixed in patch #4 though, so I'm not too concerned.
> > > >=20
> > > > Does that fix also need to be backported?
> > >=20
> > > I think so, but we might want to split that out into a more targeted
> > > patch and apply it ahead of the rest of the series. Our QA folks seem=
 to
> > > be able to hit the problem somehow, so it's likely to be triggered by
> > > people in the field too.
> >=20
> > This last paragraph requests a bit of reorganization to enable an
> > easier backport.
>=20
> I think the "error cleanup" was addressed in a different series.  Maybe
> it hasn't landed either.
>=20
> >=20
> > And on 2/5:
> >=20
> > > > > > +struct pool_private {
> > > > > > +	struct svc_serv *(*get_serv)(struct seq_file *, bool);
> > > > >=20
> > > > > This bool is pretty ugly. I think I'd rather see two operations h=
ere
> > > > > (get_serv/put_serv). Also, this could use a kerneldoc comment.
> > > >=20
> > > > I agree that bool is ugly, but two function pointers as function ar=
gs
> > > > seemed ugly, and stashing them in 'struct svc_serv' seemed ugly.
> > > > So I picked one.  I'd be keen to find an approach that didn't requi=
re a
> > > > function pointer.
> > > >=20
> > > > Maybe sunrpc could declare
> > > >=20
> > > >    struct svc_ref {
> > > >          struct mutex mutex;
> > > >          struct svc_serv *serv;
> > > >    }
> > > >=20
> > > > and nfsd could use one of those instead of nfsd_mutex and nfsd_serv=
, and
> > > > pass a pointer to it to the open function.
> > > >=20
> > > > But then the mutex would have to be in the per-net structure.  And =
maybe
> > > > that isn't a bad idea, but it is a change...
> > > >=20
> > > > I guess I could pass pointers to nfsd_mutex and nn->nfsd_serv to th=
e
> > > > open function....
> > > >=20
> > > > Any other ideas?
> > >=20
> > > I think just passing two function pointers to svc_pool_stats_open, an=
d
> > > storing them both in the serv is the best solution (for now). Like yo=
u
> > > said, there are no clean options here. That function only has one cal=
ler
> > > though, so at least the nastiness will be confined to that.
> > >=20
>=20
> We can't store the function pointers in the serv because the purpose of
> the first function is to find the serv.
>=20

Sorry, I didn't mean the serv there. You had this in the patch:

+struct pool_private {
+	struct svc_serv *(*get_serv)(struct seq_file *, bool);
+	struct svc_serv *serv;
+};

Let's just make that:

+struct pool_private {
+	struct svc_serv *(*get_serv)(struct seq_file *);
+	struct svc_serv *(*put_serv)(struct seq_file *);
+	struct svc_serv *serv;
+};

...and then just have svc_pool_stats_open take 2 function pointers. It's
not pretty but it should be fine. We have other functions that take
multiple function pointers in the kernel, so I don't see it as that bad.

> I guess I should just repost everything again....  but it isn't a good
> time for year for sustained debates.
>=20
>=20

That would be good. I'm hoping this is close to merge ready.

> > > Moving the mutex to be per-net does make a lot of sense, but I think
> > > that's a separate project. If you decide to do that and it allows you=
 to
> > > make a simpler interface for handling the get/put_serv pointers, then
> > > the interface can be reworked at that point.
> >=20
> > The other requests I see in that thread have already been answered
> > adequately.
> >=20
> >=20
> > --=20
> > Chuck Lever
> >=20
>=20

--=20
Jeff Layton <jlayton@kernel.org>